Fix install location missing in uninstall registry entry

[Copilot]

The PowerToys installer was not setting the InstallLocation value in the Windows uninstall registry entry, preventing Windows Add/Remove Programs and other system tools from properly locating the PowerToys installation directory.

Root Cause

While the installer was setting the ARPINSTALLLOCATION MSI property, this WiX approach doesn't always reliably write the InstallLocation registry value in all scenarios. The verification script even treated missing InstallLocation as "normal behavior," but this prevented proper integration with Windows system tools.

Solution

Added an explicit registry component (UninstallRegistryComponent) to both WiX 3 and WiX 5 installers that directly writes the InstallLocation value to the uninstall registry key:

<Component Id="UninstallRegistryComponent" Guid="*" Directory="INSTALLFOLDER">
  <RegistryKey Root="$(var.RegistryScope)" Key="Software\Microsoft\Windows\CurrentVersion\Uninstall\[ProductCode]">
    <RegistryValue Name="InstallLocation" Type="string" Value="[INSTALLFOLDER]" />
  </RegistryKey>
</Component>

This ensures the InstallLocation value is always written to the correct registry hive (HKLM for per-machine installations, HKCU for per-user installations) regardless of ARPINSTALLLOCATION behavior.

Changes Made

• installer/PowerToysSetup/Product.wxs: Added UninstallRegistryComponent and referenced it in CoreFeature
• installer/PowerToysSetupVNext/Product.wxs: Added UninstallRegistryComponent and referenced it in CoreFeature
• tools/Verification scripts/verify-installation-script.ps1: Updated to expect InstallLocation and report missing values as failures

Benefits

• InstallLocation is now reliably set for both per-machine and per-user installations
• Windows Add/Remove Programs can properly locate the installation
• System tools and scripts can find the installation directory through standard registry lookup
• Verification script now properly validates the installation completeness

Fixes #41638.

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